Complement Factor H-Related Proteins CFHR2 and CFHR5 Represent Novel Ligands for the Infection-Associated CRASP Proteins of Borrelia burgdorferi

Abstract

BackgroundOne virulence property of Borrelia burgdorferi is its resistance to innate immunity, in particular to complement-mediated killing. Serum-resistant B. burgdorferi express up to five distinct complement regulator-acquiring surface proteins (CRASP) which interact with complement regulator factor H (CFH) and factor H-like protein 1 (FHL1) or factor H-related protein 1 (CFHR1). In the present study we elucidate the role of the infection-associated CRASP-3 and CRASP-5 protein to serve as ligands for additional complement regulatory proteins as well as for complement resistance of B. burgdorferi.Methodology/Principal FindingsTo elucidate whether CRASP-5 and CRASP-3 interact with various human proteins, both borrelial proteins were immobilized on magnetic beads. Following incubation with human serum, bound proteins were eluted and separated by Glycine-SDS-PAGE. In addition to CFH and CFHR1, complement regulators CFHR2 and CFHR5 were identified as novel ligands for both borrelial proteins by employing MALDI-TOF. To further assess the contributions of CRASP-3 and CRASP-5 to complement resistance, a serum-sensitive B. garinii strain G1 which lacks all CFH-binding proteins was used as a valuable model for functional analyses. Both CRASPs expressed on the B. garinii outer surface bound CFH as well as CFHR1 and CFHR2 in ELISA. In contrast, live B. garinii bound CFHR1, CFHR2, and CFHR5 and only miniscute amounts of CFH as demonstrated by serum adsorption assays and FACS analyses. Further functional analysis revealed that upon NHS incubation, CRASP-3 or CRASP-5 expressing borreliae were killed by complement.Conclusions/SignificanceIn the absence of CFH and the presence of CFHR1, CFHR2 and CFHR5, assembly and integration of the membrane attack complex was not efficiently inhibited indicating that CFH in co-operation with CFHR1, CFHR2 and CFHR5 supports complement evasion of B. burgdorferi.

Bacterial Heterogeneity Is a Requirement for Host Superinfection by the Lyme Disease Spirochete

“…The possibility that innate immunity can prevent homologous, but not heterologous, B. burgdorferi infection is surprising considering that the innate system is not thought to be able to differentiate between variations that exist among heterologous bacterial strains. However, as an example, various B. burgdorferi strains may simply differ in their ability to bind host complement negative regulators (e.g., factor H and factor H-like proteins) (66)(67)(68) and/or express their own functional complement inhibitors (e.g., CspA) (69). Thus, a disparate ability of a B. burgdorferi strain to inhibit overall activation of the innate system may ultimately predetermine the partial success of host superinfection.…”

The Serology Diagnostic Schemes in Borrelia burgdorferi Sensu Lato Infections – Significance in Clinical Practice

“…The innate defense mechanisms are initiated as the first in the process of the immunological response of an organism against infection, in which as well as phagocytes as complement system, lysozyme and interferon take part. All disorders of the unspecific mechanisms in the early stage of the infection can prevent from an effective elimination of the pathogen in further stages of the immunological response, and consequently lead to the development of a chronic state of the illness (Bykowski et al, 2008;Siegel, et al, 2010). The diagnosis of the illness in patients with EM is usually made on the basis of a clinical picture without a confirmation of the serological tests, which results are frequently negative during this period.…”

“…The complement system participates in the elimination of B. Burgdorferi, and its activation on the surface of the pathogen leads to the cytolitical damage of bacteria (Bykowski, et al, 2007). The disactivation of activation cascades of the complement allows Borrelia to survive and also determines a competent reservoir for particular genospecies of bacteria (Siegel, et al, 2010). There are also other microorganisms apart from Borrelia burgdorferi, like: Echinococcus granulosus, Neisseria meningitidis, Neisseria gonorrhoeae, Streptococcus pyogenes, Streptococcus pneumoniae, Yersinia enterocolitica, Candida albicans and human immunodeficiency viruses which have developed mechanisms allowing to overcome the destructive process of the complement system.…”

“…The spirochetes induce oxidative burst and calcium mobilization and are susceptible to phagocytosis dependent on the complement (Suchonen, et al, 2000(Suchonen, et al, , 2002Krajczy, et al, 2001). The lack of susceptibility to the effect of the mechanisms of innate immunity, end especially the immunity on the destruction with the use of the complement, is determined as the virulent factor of Borrelia burgdorferi (Siegel, et al, 2010).…”

Human C3 glomerulopathy provides unique insights into complement factor H–related protein function

“…10). For example, FHR2 and FHR5 are captured by the complement regulator-acquiring proteins (CRASPs) of serum-resistant Borrelia burgdorferi and modulate complement activation (22). Further work to explore the roles of FHR interactions with pathogens will benefit our understanding of the diverse roles these proteins play in the innate immune response.…”